The present invention relates generally to fuel supply aggregates. More particularly, it relates to a fuel supply aggregate of an internal combustion engine of a motor vehicle.
In the above mentioned supply aggregates, mainly volumetric pumps, such as substantially toothed gear pumps have been used. These pumps operate with a revolution frequency of several tens hertz and produce a noise spectrum which is dominated by the revolution frequency and several low harmonics. This noise can be dampened by a vibration-dampening suspension of the supply pump without difficulties. Therefore, it can be no longer heard in addition to the running noise of the simultaneously operating the internal combustion engine.
The manufacturing cost for a fuel supply aggregate can be reduced and its reliability can be increased when instead of the volumetric pump, a rotary pump can be used. For example, such a pump can be used which during its pump action on the at least one rotatable impeller provides an acceleration applied to the fluid to be pumped.
Rotary pumps because of their construction have a different noise spectrum than volumetric pumps. A rotary pump for use in a fuel supply aggregate must be compact, and therefore the diameter of the impeller must be small. In order to obtain however the required pumping action, the impeller must rotate with high speed and must carry on its periphery a great number of vanes, frequently 40-80 pieces in order to move the fluid to be pumped. The running noise of these pumps has not only a portion of the rotation frequency of the impeller and several low harmonics, but also additionally a portion of a frequency which corresponds to the product of the rotary speed and the number of the vanes. The last portion forms a high frequency whistle tone with a frequency up to 16 kHz which is found by many people as unacceptable. Since such a frequency portion is not contained in the running noise of an internal combustion engine supplied by the fuel aggregate, it is clearly heard at low intensities.
The disadvantage of the rotary pumps prevented their use in fuel supply aggregates, in particular for motor vehicles. It has been attempted to fight the vessel noise by a different design of the vanes of the impeller and an irregular arrangement of the vanes on the impeller. As a result the spectrum of the vessel noise is wider, the noise is thereby similar to a high frequency noises, and is no longer so penetrating. However, the high frequency noise remains still hearable.
The solution, when compared to a rotary pump with a uniformly shaped impeller, is relatively costly. The reason is that the manufacture of the non uniformly shaped impeller is substantially more expensive and its imbalance requires an increased care.